The invention relates generally to magnetic resonance imaging (MRI) systems. In particular, the invention relates to a terminal board end connector for the construction of a folded gradient coil in a MRI system.
The embodiments described here are particularly directed to the construction of a folded gradient coil in an MRI system. However, its application can be expanded to other areas in which there is a need for complicated leads or coil connections and which has a limited space to assemble them, such as an electric machine with a closed slot structure.
Magnetic Resonance Imaging (MRI) is a non-invasive method, based on the physical phenomenon of nuclear spin resonance to obtain the image of the inside of an object. It has been employed for many years in the past in the field of chemistry to identify the atomic constituents in the sample material. In the past 20 years, MRI has been successfully introduced into medical imaging to demonstrate pathological or other physiological alternations of living tissues. Now its medical and diagnostic applications appear to be numerous and significant.
During the imaging process of MRI, an object is exposed to a strong constant magnetic field. This aligns the nuclear spins of the atoms in the object, which were previously oriented irregularly. Radio-frequency waves can now excite these “ordered” nuclear spins to a specific oscillation (resonant frequency). In MRI, this oscillation generates the actual measuring signal (RF response signal), which is picked up by suitable receiving coils.
The foregoing medical imaging techniques are generally implemented via a magnetic resonance imaging (MRI) apparatus such as that shown in FIG. 1 that illustrates a structure of an MRI apparatus 10 that includes a magnetostatic field magnet unit 12, a gradient coil unit 13, an RF coil unit 14, an RF driver unit 22, a gradient coil driver unit 23, a data acquisition unit 24, a controller unit 25, a patient bed 26, a data processing unit 31, an operating console unit 32, and a display unit 33. The magnetic resonance imaging apparatus 10 transmits electromagnetic pulse signals to a subject 16 placed in an imaging space 18 with a magnetostatic field formed to perform a scan for obtaining magnetic resonance signals from the subject 16 to reconstruct an image of the slice of the subject 16 based on the magnetic resonance signals thus obtained by the scan.
The magnetostatic field magnet unit 12 includes, for example, typically an annular superconducting magnet, which is mounted within a toroidal vacuum vessel. The magnet defines a cylinder space surrounding the subject 16, and generates a constant primary magneto static field, along the Z direction of the cylinder space.
The magnetic resonance imaging (MRI) apparatus 10 also includes a gradient coil unit 13 that forms a gradient field in the imaging space 18 to add positional information to the magnetic resonance signals received by the FR coil unit 14. The gradient coil unit 13 includes three magnet systems, each of which generates a gradient magnetic field which inclines into one of three spatial axes perpendicular to each other, and generates a gradient field in each of frequency encoding direction, phase encoding direction, and slice selection direction in accordance with the imaging condition. More specifically, the gradient coil unit 13 applies a gradient field in the slice selection direction of the subject 16, to select the slice; and the RF coil unit 14 transmits an RF pulse to a selected slice of the subject 16 and excites it. The gradient coil unit 13 also applies a gradient field in the phase encoding direction of the subject 16 to phase encode the magnetic resonance signals from the slice excited by the RF pulse. The gradient coil unit 13 then applies a gradient field in the frequency encoding direction of the subject 16 to frequency encode the magnetic resonance signals from the slice excited by the RF pulse.
The gradient coil unit 13 can employ known gradient coil structures such as a conventional gradient coil that employs a separate primary coil portion and a separate shield coil portion. A conventional folded gradient coil such as the coil 40 depicted in FIG. 2 can also be employed to formulate the gradient coil unit 13. The folded gradient coil 40 has a primary coil portion 42 and a shield coil portion 44 that are connected via a folded portion 46 to provide a single gradient coil per axis. The folded coil structure advantageously provides for lower inductance, lower resistance, and a less leakage magnetic field as compared with the conventional structure that has two separated gradient coils.
The transverse folded gradient coils, X and Y necessarily have to intercross with one another to ensure symmetry and optimize coil efficiency. Ideally, the coil stack-up structure should be Y_shield, X_shield, Y_primary, X_primary. Manufacturing limitations such as spatial interferences associated with the folded part 46 of the coil prevent construction of such an ideal coil stack-up structure, resulting in a coil stack-up structure having a Y_shield, X_shield, X_primary, Y_primary sequence. The resultant stack-up structure causes nonsymmetry, lowers the gradient coil efficiency, and creates a higher complexity of manufacturing requiring special parts to support the folded portion(s) 46 of the coil in which both the Y_shield and Y_primary coils lie on the cylinder surface.
A need therefore exists for a gradient coil structure that is easy to manufacture and that does not require special parts to support the folded portions of the gradient coil.